Along with an increase in the demand for bioethanol fuels, the import price of feed grains from overseas has increased drastically, which has imposed heavy burden on livestock businesses in Japan. In this situation, in order to enhance domestic production and self-sufficiency rate of feeds, not paddy rice but alternate crops are cultivated by utilizing fallow fields and so forth. However, paddy fields suitable for cultivating these alternate crops are limited due to problems such as poor drainage. For this reason, use of rice as feeds and developments of exclusive feed-rice cultivars having a high productivity (high yielding cultivars) have been promoted. In order for such high yielding cultivars to demonstrate their characteristic high-yielding properties and stable growability, and also to improve the palatability and nutritional value of livestock, weed control in the cultivation paddy fields is an important cultivation management technique (NPL 1). Further, stable and economical productions of not only high yielding cultivars and rice but also crops require low-cost, energy-saving and easy weed control. Development and use of a highly selective herbicide are effective in such control (NPL 2). Hence, required are development and cultivation of crops resistant to the herbicide used.
Meanwhile, in the weed control in cultivation paddy fields, sulfonylurea (SU) herbicides are widely employed because the herbicides are effective against a wide range of weeds at a low dose and have little influence on human and also on the environment. Nevertheless, emergence of weeds such as Scirpus juncoides Roxb. having tolerance to SU herbicides has been recognized. This brings about a problem in the cultivation management for rice and so on.
Recently, as the measure against such a problem, herbicide components such as benzobicyclon (BBC), mesotrione, and tefuryltrione have been developed, which are also effective against plants tolerant to SU herbicides and have been put into practical use. All of BBC, mesotrione, and tefuryltrione are agents for inhibiting a function of 4-hydroxyphenylpyruvate dioxygenase (4-HPPD) (4-HPPD inhibitors). Inhibiting a function of this enzyme indirectly inhibits a carotenoid synthetic system and causes chlorophyll degradation to thereby whiten and wither the plant to death (see FIG. 1). The safety of these inhibitors against food rice cultivars has been sufficiently confirmed, so that the inhibitors are rapidly widespread in rice cultivation.
However, susceptibility of high yielding cultivars to the 4-HPPD inhibitors was not examined sufficiently at the developmental stage or other stages. By now, it has been reported that seven high-yielding feed rice cultivars are susceptible to 4-HPPD inhibitors and may be withered to death in some cases (NPLs 1 and 3).
Developments of a method capable of surely identifying the resistance or susceptibility to a 4-HPPD inhibitor and a method capable of increasing the resistance or susceptibility to a 4-HPPD inhibitor would make it possible to utilize a 4-HPPD inhibitor for control of a germination risk (problem from fallen seeds and seedlings) of “self-sown seeds” from the previous year in crop rotation cycles with food and feed rice cultivars as shown in FIG. 2, for example; consequently, production expansion of the feed rice cultivar and so forth can be expected. In addition, by utilizing these methods, a 4-HPPD inhibitor may be also used in an area management technique for cultivating crops such as rice, as necessary. Furthermore, if a gene serving as a marker for identifying resistance or susceptibility to a 4-HPPD inhibitor is found out, crops including rice can be bred efficiently.
Accordingly, it has been strongly desired to develop a technique for providing a plant with resistance or susceptibility to a 4-HPPD inhibitor and a technique for determining whether a plant has resistance or susceptibility to a 4-HPPD inhibitor. However, techniques which can efficiently achieve these purposes have not been developed yet.